The invention relates to a procedure for detecting the motion properties of microparticles being fired by a microdispenser unit onto a target, in particular to a procedure for detecting the impact points and velocities of microparticles, and a position calibration procedure for a microdispenser unit with a plurality of individual microdispensers. The invention also relates to devices for implementing the procedure, and a device for microparticle detection.
It is generally known to place the smallest substance or solution quantities on a substrate in the form of small, solid particles or droplets (microparticles) using a microdispenser device. The microdispenser device enables the targeted pipetting of specific volumes and positioning on appropriately determined location coordinates. To sequentially place various substances, a microdispenser device usually has a dispensing head with several dispensers, which are set up to position the respective substances. The target positions of the dispensed particles must be precisely known to be able to position the substances in the precise location, e.g., for reaction purposes or to generate defined microsubstance patterns.
The position of a dispensing head relative to a target substrate can usually be manipulated by means of an adjustment device, with which specific head positions can be set. When the individual dispensers of the dispensing head are fixed in place, they have defined reference positions, which arise from the head position and relative arrangement of the respective dispenser relative to a reference dispenser. The practical application of dispensing heads shows that, at given reference positions of the dispenser, impact points are formed on the substrate target whose relative coordinates do not correspond to the relative coordinates of the dispensers. FIG. 8 explains this diagrammatically based on a dispenser series 30. The individual dispensers 30a, 30b, 30c, . . . are arranged in a straight row. These can be micropipettes or the like, from which microdrops are shot onto a substrate 60. The impact points 61a, 61b, 61c are no longer arranged in a straight row due to minimal misalignments of the dispensers or mechanical instabilities, as can be discerned particularly well in the bottom portion of FIG. 8 from the superposition of dispenser positions and impact points. This behavior is problematical particularly in those cases where a first substance is fired at the substrate from a first dispenser, and a second substance is to be fired from a second dispenser at precisely the same substrate position as the first substance after subsequent movement by the dispenser head. To this end, the adjustment device of the dispensing head needs information about the corresponding dispensing head positions relative to the impact point to go along with the relative dispenser positions.
As is generally known, optical systems have thus far been used to determine the impact points or target positions of dispensed liquids. For example, in a stroboscopic procedure (A. Schober et al. in xe2x80x9cBioTechniquesxe2x80x9d, Vol. 15, 1993, p. 324 ff), the drop outline is determined with a first camera, and the target position of the respective drop to be observed is determined with a second camera. As an alternative, a substance pattern generated on a substrate can be optically analyzed. A disadvantage of these detection systems in addition to the high equipment-related outlay involved is that technically complex image recognition processes would be required for automation purposes. This results in a high cost intensity for conventional systems, along with a high susceptibility to errors given their complexity. Due to the resultant unreliability, conventional microdispensing systems have had a narrow range of application in combinatorial chemistry, despite the high technological potential for use in processing highly parallel analytical tasks.
Problems in detecting the motion of dispensed particles are encountered not only in the xe2x80x9cdrop-on-demandxe2x80x9d technique illustrated above, but generally in all microparticle placement or shooting devices with which microparticles are to be deposited on specific positions in a target range along predetermined paths.
The object of the invention is to provide an improved procedure for detecting the motion properties of microparticles, in particular of their impact points and/or velocities on target substrates, which is highly reliable and easy to implement. The object of the invention is also to provide a device for implementing such a procedure, in particular an improved microparticle detector device.
The object of the invention is achieved with a procedure and device with the features described in claims 1, 6 and 10. Advantageous embodiments of the invention derive from the subclaims.
According to the invention, the impact points of the microparticles, the relative coordinates of the impact points and/or their deviation from the relative coordinates of the dispenser positions are detected with a particle detector device, which exhibits two linear-bound interactive areas defining a target plane, and is adapted to emit a detector signal as soon as a microparticle enters one of the interactive areas. In a procedure according to the invention, a dispensing head with numerous dispensers, of which one dispenser emits a sequence of microparticles as a reference dispenser, is first moved along two straight, parallel paths over the detector device in such a way that the rows of drops formed by the microparticle sequence impact said interactive areas at four reference impact points. The dispensing head coordinates respectively set with the adjustment device are determined at the reference impact points as reference dispenser coordinates. In a measuring step, the dispensing head is then moved over the detector device along a measuring path that matches one of the calibration paths or runs parallel to one of them, so that one of the remaining dispensers (measuring dispensers) emits a sequence of microparticles when one of the interactive areas is reached. As soon as a microparticle from a measuring dispenser impacts an interactive area, the measuring dispenser position relative to the position of the dispensing head is determined, and the impact point on the interactive area is ascertained from that. Finally, the distance between the relative coordinates of the microparticle impact point from the measuring dispenser and the corresponding measuring dispenser position yields the sought deviation between the arrangement of the impact point of the microparticle from the measuring dispenser relative to the reference dispenser impact point on the one hand, and the arrangement of the measuring dispenser relative to the reference dispenser on the other.
According to a preferred configuration of the invention, the determined relative deviation coordinates are used to generate a control signal for the adjustment device of the dispensing head to correct the positioning of a dispenser relative to a specific substrate location, always as a function of the expected impact point from the dispenser in question.
Depending on the interactive area layout, the microparticle velocity can also be ascertained in addition to the aforementioned motion parameters.
Viewed from a first aspect, a device according to the invention is formed by the mentioned detector device with two linear bound interactive areas that fix a target plane. Depending on the underlying measuring principle, the detector device is designed as an electro-acoustic sensor or electro-optic sensor. In the case of an electro-acoustic sensor, each of the interactive areas not parallel to each other is formed by an oscillating element with at least one straight boundary, wherein, when this boundary is reached by one microparticle out of the sequences of microparticles formed along the cited paths, a mechanical oscillation is triggered in the oscillating element. A sound converter is used to convert the mechanical oscillation into a detector signal, which, after suitable signal processing, indicates the interactive area that was hit by a microparticle. The oscillating element preferably is shaped like a tensioned elastic thread connected with a membrane of a microphone that acts as the sound converter. In this case, the detector device has two straight, fixed threads aligned at a predetermined angle (xe2x89xa00), preferably made out of metal, which fix the target plane and are each connected with a microphone. When designed as an electro-optic sensor, each interactive area is formed by a straight, parallel light beam (e.g., laser light). The impact of a microparticle in the interactive area is detected by means of a photoelectric element, e.g., a quick-acting photodiode, with which a transmission change in the optical path length or scattered light measurement is executed.
Viewed from another aspect, a device according to the invention consists of a combination of the cited detector device with a signal processing circuit and locator, which interact with an adjustment device of a dispensing head. Such an arrangement is preferably used to calibrate the impact points of a group of dispensers in a dispensing head.
The advantage to the invention is that the impact points of a dispensing head or a corresponding microparticle placement device can be determined fully automatically, rapidly and reliably. The position is determined with a simple detector, avoiding conventional image recognition procedures. In addition to the high sensitivity during individual particle detection, the advantages to the invention also include noise immunity, speed, accuracy and the relatively low costs of the detector.